Clean up deprecations that were until 6.0

[kategengler]

Clean up and remove code gated by deprecations that were until: 6.0.

• DEPRECATE_IMPLICIT_ROUTE_MODEL
• DEPRECATE_TEMPLATE_ACTION
• DEPRECATE_COMPONENT_TEMPLATE_RESOLVING
• DEPRECATE_ARRAY_PROTOTYPE_EXTENSIONS -- this one is atypical and requires more digging to figure out what needs to be removed and what tests need to be updated

For each deprecation, you'll find calls to deprecateUntil with the deprecation, for example:

deprecateUntil(`Usage of the \`{{action}}\` modifier is deprecated. Migrate to native functions and function invocation.`,
DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION);

These calls and everything in that code path should be removed. As of 6.0, these calls with until: 6.0 behave as throws so none of the code in that path is in use.

There are also calls to testUnless with the deprecations, like so:

`${testUnless(DEPRECATIONS.DEPRECATE_TEMPLATE_ACTION.isRemoved

These tests can be removed.

Finally, the deprecations themselves should be removed from deprecations/index.ts.